The present invention relates to fuser apparatus for electrostatographic printing machines and in particular to a roll fuser release agent delivery method.
In electrostatographic reproducing apparatus commonly used today, a photoconductive insulating member is typically charged to a uniform potential and thereafter exposed to a light image of an original document to be reproduced. The exposure discharges the photoconductive insulating surface in exposed or background areas and creates an electrostatic latent image on the member which corresponds to the image contained within the original document. Alternatively, a light beam may be modulated and used to selectively discharge portions of the charged photoconductive surface to record the desired information thereon. Typically, such a system employs a laser beam. Subsequently, the electrostatic latent image on the photoconductive insulating surface is made visible by developing the image with developer powder referred to in the art as toner. Most development systems employ developer which comprises both charged carrier particles and charged toner particles which triboelectrically adhere to the carrier particles. During development, the toner particles are attracted from the carrier particles by the charged pattern of the image areas of the photoconductive insulating area to form a powder image on the photoconductive area. This toner image may be subsequently transferred to a support surface such as copy paper to which it may be permanently affixed by heating or by the application of pressure or a combination of both.
In order to fix or fuse the toner material onto a support member permanently by heat, it is necessary to elevate the temperature of the toner material to a point at which constituents of the toner material coalesce and become tacky. This action causes the toner to flow to some extent onto the fibers or pores of the support members or otherwise upon the surfaces thereof. Thereafter, as the toner material cools, solidification of the toner material occurs causing the toner material to be bonded firmly to the support member.
One approach to thermal fusing of toner material images onto the supporting substrate has been to pass the substrate with the unfused toner images thereon between a pair of opposed roller members at least one of which is internally heated. During operation of a fusing system of this type, the support member to which the toner images are electrostatically adhered is moved through the nip formed between the rolls with the toner image contacting the fuser roll thereby to affect heating of the toner images within the nip. Typical of such fusing devices are two roll systems wherein the fusing roll is coated with an abhesive material, such as a silicone rubber or other low surface energy elastomer or, for example, tetrafluoroethylene resin sold by E. I. DuPont De Nemours under the trademark Teflon. In these fusing systems, however, since the toner image is tackified by heat it frequently happens that a part of the image carried on the supporting substrate will be retained by the heated fuser roller and not penetrate into the substrate surface. This tackified toner may stick to the surface of the fuser roll, offset to a subsequent sheet of support substrate, offset to the pressure roll when there is no sheet passing through a fuser nip resulting in contamination of the fuser roll, pressure roll and marked copies.
It has also been proposed to provide toner release agents such as silicone oil, in particular, polydimethyl silicone oil, which is applied on the fuser roll to a thickness of the order of about 1 micron to act as a toner release material. These materials posses a relatively low surface energy and have been found to be materials that are suitable for use in the heated fuser roll environment. In practice, a thin layer of silicone oil is applied to the surface of the heated roll to form an interface between the roll surface and the toner image carried on the support material. Thus, a low surface energy, easily parted layer is presented to the toners that pass through the fuser nip and thereby prevents toner from adhering to the fuser roll surface.
Various systems have been used to deliver release agent fluid to the fuser roll including the use of oil soaked rolls and wicks with and without supply sumps as well as oil impregnated webs. The oil soaked rolls and wicks generally suffer from the difficulty in that they require a sump of oil to replenish the roll and the wick as its supply of release agent is depleted by transfer to the fuser roll. Furthermore, a wick suffers from the difficulty of a relatively short life of the order of around 10,000 prints. Furthermore, these systems suffer from the further difficulty in that their surfaces in contact with the fuser roll are constant whereby contamination particularly by toner and paper can readily occur further reducing valuable life. The web systems, on the other hand, generally suffer from the difficulty in uniformly contacting the fuser roll to consistently apply the release agent fluid. In addition, the web systems are often complex, relatively expensive, mechanical arrangements including extra rolls and mechanical linkage.